[SOLVED] Astable IC555 in astable mode to get 100Khz frequecy

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milind.a.kulkarni

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Hi to All,

I had tried to make a IC555 chip to generate 100 to 50 Khz frequency I had selected the correspoding resistance RA and RB of 10k POT and 2k POT where I got the capacitor of 0.1nf that is 100PF.....by the computation formula for .....There was no frequecy generation at all....Is there is restriction to use the Capacitors in micro-farad range only ?....... Any help is appericated ....Thanks in advance.....
 

Standart 555 datasheet does not show lower capacitance values than 1nF
**broken link removed**

still there is 100kHz oscillators with 100pF
**broken link removed**


I suggest to use CMOS version 555, when frequency is near 100kHz or with small duty cycles

......3 MHz astable frequency capability
**broken link removed**
 
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Hi Kak111 ,

QUASAR project kit is really good information

thanks for that

regards,

milind
 

An obsolete application note (AN170) is quite definite about capacitor size:
Source: AN170
Capacitor size has not proven to be a legitimate design criteria. Values ranging from picofarads to greater than one thousand microfarads have been used successfully.
Click to expand...

However, there are cautions about resistor sizes:
In selecting the values for the timing resistors and capacitor, several points should be considered. A minimum value of threshold current is necessary to trip the threshold comparator. This value is 0.25mA.
Click to expand...

There are also cautions about those configurations that give less than 50% duty cycle. If you still cannot get it to work, please post your circuit here.
The current NXP Semiconductor datasheet ( **broken link removed**) has most, but not all that was in the earlier AN170.

John

Here is a link to the obsolete AN170:
 
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